RF probes provide temporary electrical contacts between electrical test equipment and very small selected points on an integrated circuit. The use of such probes permits operation and testing of integrated circuit (IC) elements prior to separating, bonding, or packaging of the individual trips contained on the wafer.
However, such prior art probes are generally not suitable for some applications, such as the testing of microstrip microwave integrated circuits (MMIC). MMICs typically include a ground plane on which a microstrip transmission line is placed. The transmission line is constructed typically from an alumina substrate on which the microstrip conductors are arranged to interconnect microwave devices.
A disadvantage and limitation of known prior art probes is that a high quality electrical contact from the probe tip to the microstrip circuit is not always possible. Since the microstrip circuit conductor to which the probe test must make contact is elevated with respect to the ground plane, the dimension of this elevation must be designed into the probe tip so that the electrical contact does not have any discontinuity which could cause unwanted reflections of an RF signal along with the resultant errors in measurement caused by such reflections. However, perfect matching of the probe tip to the MMIC is extremely difficult to maintain. For example, the dielectric substrates may have slight variation in thickness from each other which results in the probe tip not contacting one or the other of the MMIC microstrip signal conductor or ground plane. Also, the orientation angle of the probe tip to the MMIC may not always be constant, also causing discontinuities in the RF signal path.